Of course, someone just had to dress one. You go 2,000 metres up a mountain, see an iron statue of a naked man and what do you do but put a jacket on it.

The naked man is Antony Gormley and the setting is 150 sq km in the mountains of Vorarlberg where the latest and last of his field experiments – multiple statues of the artist dotted around in cities and landscapes – was launched today.

Horizon Field is one of the most ambitious of his projects and has taken five years to pull off: 100 cast iron versions of Gormley carefully winched by helicopters into the deep summer green countryside of the Austrian Alps, all precisely positioned – give or take 5cm – at 2,039 metres above sea level. In a few months, they'll be submerged in snow. Some are easy to find and touch; others are nearly impossible to reach. None, the organisers said with optimistic confidence, are on ski paths.

The statues are meant to pose big, existential questions. Who are we? What are we? Where have we come from? Where are we going? The answer to the last, when the Guardian asked hikers on the Diedamskopf mountain, was to the top. And then to the bottom.

"We go back Saturday," added Kristof Willemans-Verdonck, from Rumbeke in Belgium, on holiday with his wife, Ann, and their two young sons. "We saw the art coming up but I know nothing about the meaning of it. What's the meaning of it?

"This kind of art of is good, it's not Panamarenko [a Belgian artist known for his models of his imaginary vehicles], which is a good thing, I'll tell you."

On another mountain, Kriegeralpe, where Gormley today formally launched the project, the Sinnett family from Buckingham were wondering if the artist was following them. "We saw his figures in New York recently," said Paul Sinnett. "And now here. We weren't seeking him out."

His wife, Diane, confessed the figures weren't yet making her think about the future of humankind. "Coming down, it does feel a bit like they're watching you."

There was, it has to be said, a bemused reaction from most walkers. Gormley forgives them. "People shouldn't know what they think," he said. "It would be very boring if they didn't think 'What the hell is thing doing here?' or 'This is completely crazy.'"

He hopes the more statues people see the more questions they might begin to ask.

The plan is that the statues stay in the alps for two years but, who knows, maybe forever. "If it was possible, it wouldn't be bad," said Gormley. "It is completely an experiment and there are very reasonable questions to be asked about is this the right thing to do to an unsuspecting mountain."

Gormley and his collaborators have spent so long on this project because there are so many groups to talk to, including landowners, hunters, environmentalists, botanists, politicians, residents, skiers and on and on.

The figures are in the sort of place where the only sound you're guaranteed to hear is the clanking of nearby cow bells, where men wear lederhosen as if they were jeans and where you expect – any second – to see Julie Andrews spinning around about to burst into song.

The project, a collaboration with the Kunsthaus Bregenz, has been hugely complicated logistically, particularly because of Gormley's insistence on the figures being in a horizontal line, and involved the Austrian army and mountain rescue teams.

Cast iron figures of Gormley have been placed around cities and landscapes from Crosby beach to London to Australia to Calabria but the alpine project is the last of them, said the artist.

In Austria, most visitors will need to take a half-hour cable journey to see them – although some are visible from roads – and they will mean different things to different people from different distances. At 100 metres, the Gormley is defiant, standing up to everything, bring it on; close up he's vulnerable, lost perhaps.

Then there is the issue of spotting a statue, only for it to move after a few minutes – just some bloke in the distance admiring the scenery.

The 100th figure in the work was today attached to a concrete ventilator shaft in Albona. "For me it is now the beginning of the experiment," Gormley said. "Can human beings do together something that is not necessary, but in some way brings an extra dimension to everyday common experience."

Gormley said the work addressed a simple question: where does the human project fit inside the bigger question of the planet's future?

"The art work is in a way less important than the work people will do with these objects. The looking, the finding, the not finding, the relationship between something you can touch, you can see, you can imagine."